Various processes have been developed for the solvent refining of coal. Much research has gone into processes for coal liquefaction, particularly when utilizing relatively expensive metal catalysts such as those including cobalt, molybdenum, nickel and tungsten. With the increasing costs of energy and the undesirable restraints on some energy sources, there has developed heightened interest in the recovery of energy stocks in the form of liquefiable fuels from coal resources known to exist in abundance in this and other countries.
Coal liquefaction processes using expensive catalysts such as those described above have been known for quite some time. Specifically, the Germans showed great activity in this area during the war years when an internal source of liquid fuels was important to that country. A similar importance to alternate liquid fuel sources now exists throughout the world. The traditional use of expensive metal catalysts in coal liquefaction has several drawbacks. Not only are the metal catalysts expensive to provide for liquefaction processes in the first instance, but their expense dictates that additional expense is undertaken in order to provide catalyst regeneration apparatus to be used in conjunction with processes involving such catalysts.
In an attempt to overcome the problem of expensive coal liquefaction catalysts, persons skilled in this art have searched for inexpensive, potentially throw-away, catalysts which can be used in coal liquefaction processes without the need for additional apparatus necessary for regeneration. Pyrite, both as an added catalyst and as an in-situ ingredient of most coals, has been recognized as having some activity in the catalysis of coal in the liquefaction process. Other inexpensive minerals have also been shown to have catalytic activity in the coal liquefaction process.
For example, in U.S. Pat. No. 2,694,622, a catalyzed reaction of petroleum oils, coal oil or even particulate solid coal is conducted in the presence of iron and iron oxide catalysts. The iron catalysts are generally used in conjunction with water as a source of hydrogen for the hydrogenation reaction. The specification also notes that the iron oxide formed from the reaction of iron and water can also react with hydrogen sulfide to produce iron sulfides.
The use of iron oxides in a co-catalyst coal conversion process is also known in the prior art. U.S. Pat. No. 3,505,204 discloses such a process wherein iron oxide is combined as a co-catalyst with an alkali or alkaline earth metal compound and steam to produce an appropriate hydrogenation environment for the conversion of coal solids to hydrocarbons.
In U.S. Pat. No. 4,134,821, a solvent refining coal liquefaction process is described in which iron oxide catalysts are utilized in conjunction with an ebullated bed reactor. This process contemplates the use of either expensive catalysts such as cobalt and molybdenum or inexpensive catalysts such as iron oxide.
The use and reuse of inexpensive pyrite hydrogenation catalysts is set forth in U.S. Pat. No. 4,222,847 which describes a coal liquefaction process. This process discloses that a recycle pyrite catalyst shows improved activity over initially used catalysts. The specification further discloses that iron oxides under repeated recycle may experience disintegration to form ferric sulfide.
Additionally, in a February 1981 Department of Energy report by Pittsburgh and Midway Coal Mining Company, DOE/et/14800-25, the use of iron oxide and pyrite in combination as a coal liquefaction catalyst is disclosed. This disclosure was specifically in the context of a study of disposable catalysts for coal liquefaction. The disclosure notes a reduction in the catalytic activity when utilizing one to one proportions of added pyrite and added iron oxide. This prior art process fails to disclose the use of any other proportions and in fact shows decreased oil production when such a catalyst system is utilized.
The drawbacks of the prior art processes for using inexpensive, expendable catalysts in a solvent refined coal liquefaction process are overcome by the process of the present invention. The achievement of a high rate of oil production is an important aspect of the present invention. The use of inexpensive co-catalysts in a novel combination and ratio provides for unexpected catalytic activity as well as a reduction in undesirable by-products of the reaction and in the consumption of expensive hydrogen.
It is an object of the present invention to provide a coal liquefaction process which uses an inexpensive co-catalyst system of iron oxide and pyrite.
It is a further object of the present invention to use the iron oxide in a stoichiometric excess of that needed to react with all sulfur available in-situ in the reaction of the liquefying coal.
It is yet another object of the present invention to eliminate hydrogen sulfide in the coal liquefaction effluent by the appropriate addition of iron oxide to fully react with such hydrogen sulfide.
It is another object of the present invention to increase the recovery of valuable oils from a coal liquefaction process by the use of a co-catalyst of iron oxide and iron sulfide in which the iron oxide is in a stoichiometric excess of that required to react with available sulfur.
It is a further object of the present invention to reduce the consumption of hydrogen in the coal liquefaction reaction.
It is yet another object of the present invention to decrease the amount of hydrocarbon gases produced in the coal liquefaction reaction.
These and other objects will be realized and more fully understood in the description of the invention which follows.